In recent years, there has been known a duplexer utilizing an acoustic wave. In such a duplexer, a distorted wave may be generated due to its nonlinearity. For example, a transmission wave and an out-of-band disturbance wave out of the transmission band and reception band are liable to be mixed resulting in the generation of a distorted wave in the reception band. This distorted wave is so-called “inter-modulation distortion (IMD)”. This distorted wave has become one of the causes of lowering the quality of communication (SN ratio) of a wireless communication device. As art concerning a distorted wave, for example there is Patent Literature 1.